Hlk-ld2410 Datasheet

[Armanda Kicks]

Justlike the LD2411S, this is a serial device with a custom protocol communicating at 256000 baud. The protocol outputs more bytes than the HLK module though. It also has a fairly similar looking Chinese only Windows app. Sensing with this module is quite good, but I am able to fool if I stand still. I will have to stand completely still for maybe 10 seconds though, so this will work for many cases. It is also quite directional.

For some incomprehensible reason, you cannot find this information on the InnosenT website. The only information you can find is the datasheet that indicates that the data is sent at 38400 baud. There is no description of the data, so anyone buying this product will be just as puzzled as I was. After a lot of searching online, I found that this project has used the device. In this paper, they show how the data is built up (5 static bytes and then some actual content), but why on earth do I have to find that in a research paper?

If you have a sensor you think I should test, please send me an email. The same applies if you are from InnosenT (or any other vendor) and want to show me where the researchers found the details on your protocol and how I could use it to detect presence and not just movement.

Presence sensing is something that was traditionally done using passive infra-red (PIR) sensors. Unlike PIR sensors, microwave sensors do not rely on thermal detection, nor do they rely on movement; in fact microwave sensors can distinguish between static and moving objects, and the objects can be cold or hot.

At home I have old microwave-based sensors as part of an alarm system, that essentially emit radio waves at a high frequency (multi-GHz), and they mix (using a cavity known as a waveguide, and a non-linear device) the received signal (reflected off objects, including humans) with the transmitted frequency, to generate a low-frequency signal that changes whenever there is any motion. Such older sensors are very sensitive, but they have disadvantages, primarily cost, and large size.

Nowadays, things have changed for the better! There are single-chip microwave devices that do it all! The antenna is now simply a trace on the PCB, rather than a large metal waveguide. The entire sensor can be extremely small and can be hidden behind panels in walls or ceilings, for instance. As a result, they are very unintrusive, and yet can provide deep insight into how an environment is being used. Unlike PIR sensors, microwave devices can detect stationary and moving objects, and can distinguish between them, and can even detect an approximate range.

The device cannot provide an object count, nor can it indicate if the object is human, although the latter can sometimes be inferred if there is movement in a known deployed location. An object count could be achieved by deploying multiple sensors to cover different portions of a larger area, or by positioning sensors near an entrance or exit perhaps, but that is not a strength of this sensor; there are better options for that, such as thermal imaging sensors!

According to the board datasheet, the chip operates transmitting RF between the range of 24.0 to 24.25 GHz. The other side of the board contains a microcontroller from a manufacturer called ZhuHai Jieli.

Just the power supply pins and the OUT pin are required for simple usage of the board. The OUT pin will go high (3.3V) whenever the sensor has detected the presence of objects. I connected a resistor and LED to it for testing.

moving energy: This is like a confidence level, depending on speed on movement I think! 100 is very confident, and 0 is not very confident. This value is only useful when the state is moving_target or combined_target.

I decided to write some code to use the LD2410 with an Arduino. The code is on GitHub, and it requires any Arduino board with a serial interface called Serial1. The Serial1 pins are connected to the LD2410 board.

Note that because the LD2410 consumes a fair amount of current, it is not recommended to power it from the 5V output from the Arduino. You may experience a temporary brownout when connecting it (I did).

Another key point is that some Arduino boards use 5V logic, whereas the LD2410 uses 3.3V logic levels. As a result, either use a 3.3V-compatible Arduino, or at the very least, just connect the LD2410 TX pin and not the RX pin, so that the LD2410 does not experience any 5V logic levels.

The MicroPython LD2410 code is on GitHub. To use it, simply install the MicroPython environment on the Pi Pico, then upload the ld2410.py file to it (the steps to do this are documented on the Raspberry Pi website).

The LD2410 is quite a nice board for detecting the presence of objects, including humans, in either static or motion states, and it is configurable to fine-tune the detection ranges. It can be set to be extremely sensitive if desired. I liked that the board is tiny, so it could be easy to conceal, making systems that are entirely invisible to users while performing valuable tasks.

A minor negative point is that the serial interface data rate is unusually high at 256 kbps. I wish it was just 115200 bps, since that is a more popular value. Still, it was possible to use the board with Python code on the PC, as will as with an Arduino, and with a Pi Pico running MicroPython.

The microwave IC manufacturer is Sidian Micro, but they also seem to be known as ICLegend Micro, at least that's their Internet presence anyway! On their website they have some documentation, but not complete datasheets without approval. However, based on the information I could find there, using Google Translate, I was at least able to confirm the decoding of the reports from their reference design, because it seems the HLK-LD2410 is a semi-clone of the reference design (with a different microcontroller, but I believe using the same code ported across - there's no access to the source code on the website however).

The first link was interesting, the product page showed that the PC app looked to be in a similar style to the one I used with the LD2410, so I followed the links, and now know what that RF chip is. It's part code S3KM111L, there's not a lot of public information on it.

Also, by googling that chip name it was possible to find an Arduino library for the LD2410. I have not tried it, but hopefully it might be better than the code I wrote, since mine was prototyped in a couple of hours.

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